1. Field of the Invention
The present invention relates to an optical waveguide lateral alignment technique and, more particularly, to an interlocking ridge and groove technique which is utilized to join together a pair of substrates and prevent motion in the lateral direction. This alignment technique is applicable to coupling a substrate containing waveguides to one containing fibers, as well as waveguide-to-waveguide coupling.
2. Description of the Prior Art
As fiber optics becomes an ever increasing choice for data, voice, and video communications, the requirements on the quality of the optically transmitted signal become more demanding. One area which has received great attention is the problem of coupling the optical signal; either between a fiber and an optical waveguide, or between a pair of optical waveguides. Indeed, a significant part of the packaging problem is due to the stringent alignment tolerances required for coupling between devices and optical fibers. To date, most applications have required the alignment of only a single fiber to a single optical device. However, with the advent of integrated optical devices, the need has arisen to align linear arrays of fibers to devices. One prior art technique for accomplishing array alignment is disclosed in U.S. Pat. No. 4,217,032 issued to S. K. Sheem on Aug. 12, 1980. The Sheem technique utilizes a two-dimensional, intersecting groove pattern formed in a silicon substrate wherein a groove in one direction is deeper than the corresponding intersecting groove, and an alignment fiber rests in the deeper groove. The shallow groove accommodates an optical fiber sized to contact the alignment fiber. The alignment fiber is tapered so that as it slides along the groove, it raises or lowers the optical fiber to a level which yields maximum optical transmission. This alignment technique becomes extremely time consuming when a large array of optical fibers must be individually aligned.
An alternative alignment arrangement which does not require individual alignment is disclosed in U.S. Pat. No. 4,196,997 issued to W.L. Schumacher on Feb. 5, 1980. The Schumacher disclosure relates to a method and apparatus for connecting optical waveguides in coincident alignment, and features a connector divided into intermating sections, each section in the form of an open box configuration provided with a projecting tongue for mating with the other section. This method is not applicable to the situation where one of the sections to be aligned contains a plurality of optical fibers.
An alternative prior art coupling technique utilizes a fiber array cover plate which has an endface coplanar with the ends of the individual fibers. This technique is disclosed in a copending application Ser. No. 621,453, filed on June 18, 1984 and assigned to the same assignee as the present application. As disclosed in Ser. No. 621,453, the use of a plurality of fibers disposed in grooves with the above-described cover plate results in an alignment technique which will automatically align five of the six possible degrees of freedom associated with coupling the fiber array to an optical waveguide substrate, the remaining degree of freedom being defined as lateral alignment, i.e., the alignment in the plane of the top surface of the substrate which is perpendicular to the direction traveled by the optical signal. Present techniques for performing this final alignment require the observation of optical throughput, where the alignment must be adjusted until maximum throughput intensity is achieved. When an array connection is required, this alignment technique becomes cumbersome and time-consuming.
Therefore, a need remains in the prior art for a technique which provides automatic lateral alignment when performing fiber-to-waveguide coupling, or alternatively, waveguide-to-waveguide coupling, which does not require a real-time observation of optical throughput.